5. COMBINING CMB AND LARGE-SCALE STRUCTURE OBSERVATIONS

As CMB anisotropy is detected on smaller angular scales and large-scale
structure surveys extend to larger regions, there is an increasing overlap
in the spatial scale of inhomogeneities probed by these complementary
techniques. This allows us to test the gravitational instability paradigm
in general and then move on to finding cosmological models which can
simultaneously explain the CMB and large-scale structure observations.
Figure 5 shows this comparison for our
compilation of CMB anisotropy observations (colored boxes) and of
large-scale structure surveys (APM -
Gaztañaga
& Baugh 1998,
LCRS -
Lin et al. 1996,
Cfa2+SSRS2 -
Da Costa et
al. 1994, PSCZ -
Tadros et
al. 1999,
APM clusters -
Tadros et
al. 1998) including
measurements of the dark matter fluctuations from peculiar velocities
(Kolatt &
Dekel, 1997)
and the abundance of galaxy clusters
(Viana &
Liddle, 1996;
Bahcall et al.,
1997).
Plotting CMB anisotropy
data as measurements of the matter power spectrum is a model-dependent
procedure, and the galaxy surveys must be corrected for redshift
distortions, non-linear evolution, and galaxy bias (see
Gawiser & Silk
1998
for detailed methodology.) Figure 5 is good
evidence that the matter and radiation inhomogeneities had a common
origin - the standard
CDM model with a
Harrison-Zel'dovich primordial power
spectrum predicts both rather well. On the detail level, however, the model
is a poor fit (2
/ d.o.f.=2.1), and no cosmological model which
is consistent with the recent Type Ia supernovae results
fits the data much better. Future observations will tell us if this is
evidence of systematic problems in large-scale structure data or a fatal
flaw of the CDM
model.